How are dry flocculants manufactured, and their mixing implications.

April 24, 2013 by Bill Hancock 0 comments

Water-soluble polymers, called flocculants, and their chemical makeup, have been the topic of discussion in the last few weeks. In this blog, we will shift our focus to discuss the two main flocculant forms. Understanding the manufacturing process and form of these products will set the tone for future discussions of proper mix and feed system design.

As previously explained, flocculants are long-chain polymers that aggregate particles together to either settle faster or improve water/solution drainage, depending on the solids/liquid (S/L) separation process used. Water-soluble polymer building blocks, called monomers, are reacted together basically end to end to make the chained polymer. There are three basic flocculant forms produced and sold:

  • Dry powder (crushed and bead forms)
  • Emulsion liquid
  • Solution liquid

Dry flocculant and primarily crushed product will be topic of discussion this week. Essentially, the process for producing dry flocculants involves the following steps:

dry flocculant manufacture process
  • Blend the different monomers with the chemistry type and charge level desired.
  • Polymerize the monomers into long chains, in a temperature- and pressure-controlled reactor with reaction initiation and termination chemicals, to the chain length and degree of branching desired. A flocculant gel is produced that is, for rough perspective, on the order of 20% polymer solids, with the balance essentially water.
  • Extrude the gel into strands, much the same as a hamburger grinder.
  • Dry the extruded flocculant to moistures ≤ 5% water. Different manufactures use different proprietary drying processes, since it is a key step.
  • Reduce the size of dried flocculants in a closed circuit with a screening classification step to get the flocculant particles into a specific size range, typically -10 mesh (2000 μ, microns) to + 100 mesh (149 μ).
  • Bag the product and ship it.

Some relevant points related to how the process impacts the final product selection and use include:

  • Since dry flocculant particles dissolve slowly from the particle surfaces, dissolution time and rate is directly related to the amount of particle surface area. Particles sized below -10 mesh will dissolve faster than larger particles.
  • Slipping on dissolved flocculant on floors and platforms is a significant safety hazard. To prevent dust drifting while handling and feeding, minimize very fine particles from dispersing. The primary control measure is to remove the very fine particles in manufacturing, which is the reason the -100-mesh flocculant fines are removed.
  • The drying step can break the polymer chains, reducing their length and ability to aggregate particles. This can be controlled by the manufacturers; however, the highest molecular weight flocculants are typically obtained with emulsion polymers that are manufactured without a drying step.

Next week we’ll discuss the proper methods for mixing and feeding dry flocculants.

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Categories: Flocculants